Exemplary materials for the cover sheets and the core sheet are disclosed in the EP1059160 which shall be made by reference to a part of this disclosure.
With these composite layer workpieces numerous advantages can be achieved in comparison to solid workpieces having the same dimensions. Very high mechanical and acoustic energy absorption can be obtained, wherein the structures furthermore can be provided with an insensitive and corrosion resistant surface depending on the type, shape, density, thickness, length and orientation of the fibers, for example a particularly low weight and a high flexural strength or a superior moldability and flexibility, respectively. All these properties can be optimized according to the proposed machining (like bending, deep-drawing, welding, cutting, etc.), as well as according to the application of the composite layer workpieces.
WO 98/01295 discloses a formable sandwich construction material which comprises at least two plates of metallic fibers. By this, a substantially higher temperature resistance shall be obtained in comparison to those structures which comprise fibers of organic materials. The manufacture, which is disclosed in the EP0333685, is conducted such that the plates are covered with an adhesive and then the metallic fibers are deposited onto at least one of the adhesive layers by acceleration by means of an electrostatic field (electrostatic flocking process) so that there are substantially perpendicularly fixed relative to the plate. Then the plates are pressed onto each other and the adhesive is hardened.
Furthermore, DE4131394 discloses a sound insulation material which is formed by two outer sheets between which a core sheet containing a filling material and a binder is provided wherein the three sheets are continuously pressed against each other during the manufacture of the sound insulation material.
DE3621599 discloses a method and a device for distributing short fiber materials onto a horizontally moved sheet-breadth wherein a funnel with a chamber is provided which has a dispensing opening for delivering fiber material through a screen sieve onto the moving sheet and wherein the screen sieve is laterally oscillating. By this, a uniform distribution of the fiber materials over the whole width of the breadth shall be obtained.
Furthermore, EP0014973 discloses a method for the manufacture of a machined part. According to this method, a foil-breadth is coated with a liquid adhesive in a first station and in a second station flock fibers are applied onto the adhesive coating by means of an electrostatic field. Afterwards the adhesive is pre-hardened by means of a heating device so that the flock fibers adhere to the adhesive in the form of a coating and the foil breadth can be pressed and pre-formed together with a supporting part.
Finally, DE3824842 discloses a heat insulating plate and a method for its manufacture in which during a continuous process an inner coating comprising lamella of a heat insulating filling material, mixed with a binder, is fed in between two shaped metal sheets and in which these three sheets are glued together by means of an adhesive which is injected in between these sheets to achieve a sandwich structure.
All these methods and a arrangements, however, have the disadvantage that either they are provided only for the manufacture of specific elements and consequently are not generally applicable, or they are not suited for a continuous production process with which a high output of pieces of sandwich structures per time unit can be manufactured.